The present invention relates to immunology and, in particular, to immunization of hosts using nucleic acid to provide protection against infection by Chlamydia.
DNA immunization is an approach for generating protective immunity against infectious diseases (ref. 1 throughout this application, various references are cited in parentheses to describe more fully the state of the art to which this invention pertains. Full bibliographic information for each citation is found at the end of the specification, immediately preceding the claims. The disclosure of these references are hereby incorporated by reference into the present disclosure). Unlike protein or peptide based subunit vaccines, DNA immunization provides protective immunity through expression of foreign proteins by host cells, thus allowing the presentation of antigen to the immune system in a manner more analogous to that which occurs during infection with viruses or intracellular pathogens (ref. 2). Although considerable interest has been generated by this technique, successful immunity has been most consistently induced by DNA immunization for viral diseases (ref. 3). Results have been more variable with non-viral pathogens which may reflect differences in the nature of the pathogens, in the immunizing antigens chosen, and in the routes of immunization (ref. 4). Further development of DNA vaccination will depend on elucidating the underlying immunological mechanisms and broadening its application to other infectious diseases for which existing strategies of vaccine development have failed.
Chlamydia trachomatis is an obligate intracellular bacterial pathogen which usually remains localized to mucosal epithelial surfaces of the human host. Chlamydiae are dimorphic bacteria with an extracellular spore-like transmission cell termed the elementary body (EB) and an intracellular replicative cell termed the reticulate body (ref. 5). From a public health perspective, chlamydial infections are of great importance because they are significant causes of infertility, blindness and are a prevalent co-factor facilitating the transmission of human immunodeficiency virus type 1 (ref. 6). Protective immunity to C. trachomatis is effected through cytokines released by Thl-like CD 4 lymphocyte responses and by local antibody in mucosal secretions and is believed to be primarily directed to the major outer membrane protein (MOMP), which is quantitatively the dominant surface protein on the chlamydial bacterial cell and has a molecular mass of about 40 kDa (ret. 16).
Initial efforts in developing a chlamydial vaccine were based on parenteral immunization with the whole bacterial cell. Although this approach met with success in human trials, it was limited because protection was short-lived, partial and vaccination may exacerbate disease during subsequent infection episodes possibly due to pathological reactions to certain chlamydial antigens (ref. 8). More recent attempts at chlamydial vaccine design have been based on a subunit design using MOMP protein or peptides. These subunit vaccines have also generally failed, perhaps because the immunogens do not induce protective cellular and humoral immune responses recalled by native epitopes on the organism (ref. 9).
In copending U.S. patent application Ser. No. 08/893,381 filed Jul. 11, 1997, (U.S. Pat. No. 6,235,290) assigned to University of Manitoba and the disclosure of which is incorporated herein by reference (WO 98/02546), I have described the generation of a protective immune response using a DNA sequence which encodes the MOMP of C. trachomatis in a plasmid by DNA immunization.
The present invention is concerned with nucleic acid immunization, specifically DNA immunization, to generate in a host protective antibodies to a serine-threonine kinase of a strain of Chlamydia. DNA immunization induces a broad spectrum of immune responses including Thl-like CD4 responses and mucosal immunity.
Accordingly, in one aspect, the present invention provides a non-replicating vector comprising a nucleotide sequence encoding a serine-threonine kinase (STK) or a fragment of STK that generates a STK-specific immune response, and a promoter sequence operatively coupled to said nucleotide sequence for expression of said STK in a host to which the vector is administered.
The promoter may be a cytomegalovirus promoter, and may be contained in the human cytomegalovirus major immediate-early promoter-enhancer region. The vector may be a plasmid vector and the nucleotide sequence may be those of SEQ ID No: 1.
The strain of Chlamydia may be a strain of Chlamydia inducing chlamydial infection of the lung, including Chlamydia trachomatis or Chlamydia pneumoniae. The non-replicating vector may be plasmid pcDNA3 into which the nucleotide sequence is inserted. The pcDNA3 vector may contain the nucleotide sequence having SEQ ID No: 1.
In a further aspect of the present invention there is provided an immunogenic composition for in vivo administration to a host for the generation in the host of a protective immune response to a serine-threonine kinase (STK) of a strain of Chlamydia, comprising a non-replicating vector as provided herein and a pharmaceutically-acceptable carrier therefor.
In an additional aspect of the invention, there is provided as a method of immunizing a host against disease caused by infection with a strain of Chlamydia, which comprises administering to said host an effective amount of a non-replicating vector as provided herein.
In these aspects of the present invention, the various options and alternatives discussed above for the non-replicating vector may be employed.
The non-replicating vector may be administrated to the host, including a human host, in any convenient manner, such as intramuscularly or intranasally.
The present invention also includes, in a further aspect thereof, a method of using a gene encoding a serine-threonine kinase (STK) of a strain of Chlamydia or a fragment of said STK that generates a STK-specific immune response, to produce an immune response in a host, which comprises isolating said gene; operatively linking said gene to at least one control sequence to, produce a non-replicating vector, said control sequence directing expression of said STK when introduced into a host to produce an immune response to said STK; and introducing said vector into a host.
In an additional aspect of the invention, there is provided a method of producing a vaccine for protection of a host against disease caused by infection with a strain of Chlamydia, which comprises isolating a nucleotide sequence encoding a serine-threonine kinase (STK) of a strain of Chlamydia or a fragment of the STK that generates a STK-specific immune response, operatively linking said nucleotide sequence to at least one control sequence to produce a non-replicating vector, the control sequence directing expression of said STK when introduced co a host to produce an immune response to said STK, and formulating said vector as a vaccine for in vivo administration to a host.
The various options and alternatives discussed above may be employed in this aspect of the invention.
Advantages of the present invention, therefore, include a method of obtaining a protective immune response to infection carried by a strain of Chlamydia by DNA immunization of DNA encoding the major outer membrane protein of a strain of Chlamydia.